Added comment to tests/ui/box/self-assignment.rs

Author: reddevilmidzy

tests/ui/box/self-assignment.rs

@@ -1,8 +1,10 @@
 //@ run-pass
+//! regression test for <https://github.com/rust-lang/rust/issues/3290>
+
 #![allow(dead_code)]
 
 pub fn main() {
-   let mut x: Box<_> = Box::new(3);
-   x = x;
-   assert_eq!(*x, 3);
+    let mut x: Box<_> = Box::new(3);
+    x = x;
+    assert_eq!(*x, 3);
 }